Shelf



FIG. 1 is a perspective view of a shelf showing my new design;

FIG. 2 is a left side view thereof, the opposite side being a mirror image of the side shown;

FIG. 3 is a front elevational view thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a bottom plan view thereof. 

The ornamental design for a shelf, as shown and described. 